(1) Field of the Invention
The present invention relates to a display device, and in particular, to a display device having an electronic circuit on the display substrate.
(2) Related Art Statement
Thin film transistors and resistor elements used as electronic circuit elements in display devices are manufactured by repeating a film formation step of forming various metal films, insulating films and semiconductor films on a glass substrate in plate form, a photolithography step of forming a photoresist pattern in order to give these films a predetermined form, an etching step of removing part of the films and leaving them in the region covered by the photoresist pattern, and a photoresist pattern removing step of removing the photoresist pattern.
However, it has become necessary to increase the size and performance of manufacturing units, because liquid crystal televisions are becoming more and more common, the size and resolution of screens are becoming larger, and power consumption has been becoming lower, and as a result, increase in power consumption and increase in the amount of materials used in the manufacture process have become a problem. Thus, less power consumption and amount of materials used has been required for manufacture, by shortening the manufacturing process for thin film transistors and resistor elements.
In order to shorten the manufacturing process for thin film transistors and resistor elements, it is most effective to reduce the number of photolithography steps. This is because reduction in the number of photolithography steps makes it possible to reduce the number of etching steps and the number of steps for removing the photoresist pattern at the same time.
A photoresist reflow technology, for example, has been proposed as a technology for reducing the number of photolithography steps (see Patent Document 1 below). In this technology, a new photoresist pattern is formed by softening the photoresist, so that the photoresist pattern changes when an organic solvent permeates into the photoresist pattern, which is formed in advance.
The photoresist reflow technology is expected to be used as a technology for forming a semiconductor layer pattern and a source/drain electrode pattern in reverse-stagger type thin film transistors, for example, in a single photolithography step.
As shown in FIG. 2A, in the photoresist reflow technology, first a gate insulating film 8, an intrinsic semiconductor thin film 9, an impurity semiconductor thin film 10 and a thin film 11 for source/drain electrodes are formed in sequence in upper layers of the insulating substrate 6 on which a gate electrode pattern 7 is formed in advance, and after that, photoresist patterns 12a and 12b are formed on the thin film 11.
Next, as shown in FIG. 2B, the thin film 11 and the thin film 10 in regions exposed from the photoresist patterns 12a and 12b are etched in sequence, so that a source electrode pattern 11a, a drain electrode pattern 11b, and ohmic contact layers 10a and 10b are formed.
Next, as shown in FIG. 2C, a new photoresist pattern 12c is formed by reflowing photoresist patterns 12a and 12b. In this case, the photoresist pattern 12c deforms during the reflow process, so that the photoresist pattern 12a on the source electrode pattern 11a and the photoresist pattern 12b on the drain electrode pattern 11b are connected.
Next, as shown in FIG. 2D, the thin film 9 in a region which is exposed from the photoresist pattern 12c is etched, so that a semiconductor layer pattern 9c is formed.
Then, as shown in FIG. 2E, the photoresist pattern 12c is removed and the process is completed.
[Patent Document 1] Japanese Unexamined Patent Publication 2007-273828